In medical X-ray imaging, segmentation of vessels is used for providing enhanced information about a vessel structure, for example. Such information can be used for assessing a health state of a patient or also for planning of a necessary intervention, but also for live guidance during an intervention, and also for an evaluation of a treatment. For example, aneurisms are commonly treated endovascularily under guidance of live X-ray. Aneurisms can be treated by placing coils in the aneurism and/or stents in a feeding vessel. A further example is the placement of a flow diverter stent. For such treatment, knowledge about the blood flow inside the vessel is needed. For example, a three-dimensional radiographic angiography acquisition is made in order to assess the vasculature, its morphology, plan the procedure, and among others, also plan the optimal viewing angles for the flow acquisition. WO 2010/018495 A1 describes colour flow imaging in X-ray. However, it has been shown that an accurate segmentation, in particular for crossing vessels and aneurisms, improves measurements of the blood flow. An example for achieving segmentation information is the provision of at least two X-ray images from different angles to achieve the depth information. However, this means an additional X-ray dose and requires either that the X-ray system be moved, in which case the segmentation data cannot be obtained at the same time as the flow acquisition, or it requires the use of multiple X-ray imagers.